1. Field
A coordinate detection device mounted on an information terminal apparatus is provided.
2. Related Art
FIG. 8 is a plan view of a capacitive coordinate detection device according to the related art. The capacitive coordinate detection device shown in FIG. 8 has a base sheet 121 having a film shape formed of a dielectric. As shown in FIG. 8, a plurality of X detection electrodes 101x, 102x, 103x, 104x, 105x, and 106x extend in a Y direction and are disposed at predetermined gaps in an X direction (electrodes that extend in the Y direction and detect an X coordinate at a position where a conductor is brought into contact with or approaches the base sheet). A plurality of common electrodes 101k, 102k, 103k, 104k, and 105k extend in the Y direction and are disposed between the X detection electrodes at predetermined gaps in the X direction and are provided on a rear surface of the base sheet 121 so as not to be brought into contact with each other. The common electrodes 101k, 102k, 103k, 104k, and 105k are connected to one another at the end of the Y2 side, and are led to the outside of the base sheet 121 as a common electrode K.
Further, as indicated by a broken line in FIG. 8, a plurality of Y detection electrodes 101y, 102y, 103y, 104y, 105y, 106y, 107y, and 108y extend in the X direction and are disposed in the Y direction at predetermined gaps (electrodes that extend in the X direction and detect a Y coordinate at a position where the conductor is brought into contact with or approaches the base sheet 121) and are provided on a surface of the base sheet 121. In FIG. 8, the common electrodes 101k, 102k, 103k, 104k, and 105k disposed on the rear surface of the base sheet 121 are indicated by solid lines.
The plurality of X detection electrodes 101x, 102x, 103x, 104x, 105x, and 106x disposed on one surface of the base sheet 121, and the plurality of Y detection electrodes 101y, 102y, 103y, 104y, 105y, 106y, 107y, and 108y disposed on the other surface of the base sheet 121 are disposed to cross at right angles to each other on both surfaces of the base sheet 121.
As shown in FIG. 8, a plurality of common branch electrodes 122 that extend toward both sides of the X direction in a straight line at a predetermined length are formed in the common electrodes 101k, 102k, 103k, 104k, and 105k. The common branch electrodes 122 are disposed to cross the common electrodes 101k, 102k, 103k, 104k, and 105k in the Y direction at predetermined gaps. The front ends of both directions (X1 and X2 directions) basically extend up to positions immediately before crossing the X detection electrodes 101x, 102x, 103x, 104x, 105x, and 106x. 
As shown in FIG. 8, the X detection electrodes 101x, 102x, 103x, 104x, 105x, and 106x are correspondingly connected to leading lines 101xa, 102xa, 103xa, 104xa, 105xa, and 106xa at the end of the Y1 side. The X detection electrodes 101x, 102x, 103x, 104x, 105x, and 106x are connected to a control IC (not shown) through the leading lines 101xa, 102xa, 103xa, 104xa, 105xa, and 106xa. 
Further, the Y detection electrodes 101y, 102y, 103y, 104y, 105y, 106y, 107y, and 108y are correspondingly connected to leading lines 101ya, 102ya, 103ya, 104ya, 105ya, 106ya, 107ya, and 108ya at the end of the X1 side. The Y detection electrodes 101y, 102y, 103y, 104y, 105y, 106y, 107y, and 108y are connected to the control IC (not shown) through the leading lines 101ya, 102ya, 103ya, 104ya, 105ya, 106ya, 107ya, and 108ya. 
In the coordinate detection device 120 shown in FIG. 8, capacitance C is coupled between each of the plurality of common electrodes 101k, 102k, 103k, 104k, and 105k and two electrodes adjacent to each common electrode among the X detection electrodes 101x, 102x, 103x, 104x, 105x, and 106x. If a voltage Vin of a pulse form is applied to each of the X detection electrodes 101x, 102x, 103x, 104x, 105x, and 106x, the voltage Vin is applied to each of the common electrodes 101k, 102k, 103k, 104k, and 105k through capacitance C.
If a conductor comes into contact with or approaches the coordinate detection device 120 in a state where a finger or the like is grounded, charges applied between the common electrode 101k, 102k, 103k, 104k, and 105k and the X detection electrodes 101x, 102x, 103x, 104x, 105x, and 106x are induced to the conductor, thereby reducing capacitance C. Accordingly, a detection voltage Vout depends on a change in capacitance C output from the X detection electrodes 101x, 102x, 103x, 104x, 105x, and 106x. The detection voltage Vout is changed according to a distance between the conductor and the X detection electrodes. It is possible to determine a coordinate position of the conductor in the X direction by sequentially detecting voltage values of the X detection electrodes 101x, 102x, 103x, 104x, 105x, and 106x at a predetermined cycle.
The plurality of common branch electrodes 122 formed in the common electrodes 101k, 102k, 103k, 104k, and 105k, and the Y detection electrodes 101y, 102y, 103y, 104y, 105y, 106y, 107y, and 108y provided between them are opposite to each other. Capacitance C is formed between the common branch electrode 122 and two adjacent Y detection electrodes in the Y direction in the same manner as the above. In the same manner as the X detection electrodes, if a pulse voltage Vin of a predetermined cycle is applied to the common electrode K and a detection voltage Vout output from the Y detection electrodes 101y, 102y, 103y, 104y, 105y, 106y, 107y, and 108y is sequentially detected at a predetermined cycle, it is possible to determine a coordinate position of the conductor in the Y direction.
The coordinate detection device 120 shown in FIG. 8 is mounted on an information terminal apparatus fixed into a case of the information terminal apparatus in a state where the base sheet 121 is in a planar shape.
The configuration in which the capacitive coordinate detection device is mounted on the information terminal apparatus in the planar shape is disclosed in JP-A-2002-123363.
Similarly to FIG. 8, in a capacitive coordinate detection device 120 of the related art, as shown in FIG. 8, a gap between adjacent leading lines 101xa, 102xa, 103xa, 104xa, 105xa, and 106xa is set to be smaller than a gap between the X detection electrodes 101x, 102x, 103x, 104x, 105x, and 106x. The leading lines 101xa, 102xa, 103xa, 104xa, 105xa, and 106xa extend to be close to an operation region that has the X detection electrodes 101x, 102x, 103x, 104x, 105x, and 106x in a direction that crosses the X detection electrodes.
If a conductor such as a finger or the like moves up to the end of the Y1 direction in the operation region, the conductor approaches the leading lines 101xa, 102xa, 103xa, 104xa, 105xa, and 106xa, and then charges of the leading lines are induced to the conductor. An error may occur in position detection in an X coordinate direction.
The leading lines 101ya, 102ya, 103ya, 104ya, 105ya, 106ya, 107ya, and 108ya obliquely extend from the end of the X1 side of the Y detection electrodes 101y, 102y, 103y, 104y, 105y, 106y, 107y, and 108y. 
If the conductor moves up to the end of the X1 direction in the operation region, since the conductor approaches the obliquely extending leading lines, an error may occur in position detection in a Y coordinate direction.
When the leading lines 101xa, 102xa, 103xa, 104xa, 105xa, and 106xa are provided to be spaced apart from the operation region or when the leading lines 101ya, 102ya, 103ya, 104ya, 105ya, 106ya, 107ya, and 108ya are provided to be spaced apart from the operation region, the erroneous detection can be reduced or prevented. The area of the base sheet 121 needs to be made large, and thus the size of the coordinate detection device 120 increases. Accordingly, the coordinate detection device cannot be properly mounted on a small information terminal apparatus.